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The conserved protein EF4 (LepA) modulates the elongation cycle of protein synthesis.

ABSTRACT: EF4 (LepA), a strongly conserved protein, is important for bacterial growth and functional protein biosynthesis under certain conditions and is quite similar structurally to the translocase EF-G. The elongation cycle in protein synthesis is characterized by ribosome oscillation between pretranslocation (PRE) and posttranslocation (POST) complexes. Here, using ensemble single turnover and equilibrium experiments, as well as single molecule FRET measurements, we demonstrate that EF4 can compete with EF-G for binding to the PRE complex. Such EF4 binding results in formation of a complex, denoted X(3), that effectively sequesters a catalytically active ribosome, leading to a transient inhibition of elongation that provides a mechanism for optimization of functional protein synthesis. Earlier [Liu H, et al. (2010) J Mol Biol 396:1043-1052] we demonstrated that EF4 also reacts with POST complex, leading to the formation of a complex, I(3), that appears to be identical with X(3). Our present results strongly suggest that PRE complex is the principal target of EF4 action on translation, rather than POST complex as had been previously supposed.

SUBMITTER: Liu H

PROVIDER: S-EPMC3182707 | biostudies-literature | 2011 Sep

REPOSITORIES: biostudies-literature

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Project description:The recalcitrance of mycobacteria to antibiotic therapy is in part due to its ability to build proteins into a multi-layer cell wall. Proper synthesis of both cell wall constituents and associated proteins is crucial to maintaining cell integrity, and intimately tied to antibiotic susceptibility. How mycobacteria properly synthesize the membrane-associated proteome, however, remains poorly understood. Recently, we found that loss of lepA in Mycobacterium smegmatis (Msm) altered tolerance to rifampin, a drug that targets a non-ribosomal cellular process. LepA is a ribosome-associated GTPase found in bacteria, mitochondria, and chloroplasts, yet its physiological contribution to cellular processes is not clear. To uncover the determinants of LepA-mediated drug tolerance, we characterized the whole-cell proteomes and transcriptomes of a lepA deletion mutant relative to strains with lepA We find that LepA is important for the steady-state abundance of a number of membrane-associated proteins, including an outer membrane porin, MspA, which is integral to nutrient uptake and drug susceptibility. Loss of LepA leads to a decreased amount of porin in the membrane which leads to the drug tolerance phenotype of the lepA mutant. In mycobacteria, the translation factor LepA modulates mycobacterial membrane homeostasis, which in turn affects antibiotic tolerance.ImportanceThe mycobacterial cell wall is a promising target for new antibiotics due to the abundance of important membrane-associated proteins. Defining mechanisms of synthesis of the membrane proteome will be critical to uncovering and validating drug targets. We found that LepA, a universally conserved translation factor, controls the synthesis of a number of major membrane proteins in M. smegmatis LepA primarily controls synthesis of the major porin MspA. Loss of LepA results in decreased permeability through the loss of this porin, including permeability to antibiotics like rifampin and vancomycin. In mycobacteria, regulation from the ribosome is critical for the maintenance of membrane homeostasis and, importantly, antibiotic susceptibility.

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The conserved protein EF4 (LepA) modulates the elongation cycle of protein synthesis.

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